* Support the standard ctrl-v <literal> control sequence. Otherwise there
is no way to do this from the venerable telnet vty. vtysh supports this
(configurably) via readline.
* lib/vty.c: (VTY_ESC_LITERAL) New mode, for ctrl-v.
(vty_read) Additional mode to go ctrl-v -> VTY_ESC_LITERAL, and
always insert next char.

* vty.c: Fix str* overruns in previous commit, which I reported to the
author. Add bit more checking of updates to vty buffer.
Swap VTY_BUFSIZ over to vty->max, as that should be the external API.
* vty.c: (vty_buf_assert) conditions that should always be assertable for
vty buffer.
(vty_buf_put) little wrapper to check char puts to vty input buffer,
and unconditionally write nul at very end of buffer as guard.
Won't always work, as some places use mem* to manipulate.
(vty_self_insert{,_overwrite}) Length check needs to leave room for nul.
Use vty_buf_put.
(vty_insert_word_overwrite) Length check needs to leave room for nul.
(*) Add vty_buf_assert calls.

* Support the standard ctrl-v <literal> control sequence. Otherwise there
is no way to do this from the venerable telnet vty. vtysh supports this
(configurably) via readline.
* lib/vty.c: (VTY_ESC_LITERAL) New mode, for ctrl-v.
(vty_read) Additional mode to go ctrl-v -> VTY_ESC_LITERAL, and
always insert next char.

* vty.c: Fix str* overruns in previous commit, which I reported to the
author. Add bit more checking of updates to vty buffer.
Swap VTY_BUFSIZ over to vty->max, as that should be the external API.
* vty.c: (vty_buf_assert) conditions that should always be assertable for
vty buffer.
(vty_buf_put) little wrapper to check char puts to vty input buffer,
and unconditionally write nul at very end of buffer as guard.
Won't always work, as some places use mem* to manipulate.
(vty_self_insert{,_overwrite}) Length check needs to leave room for nul.
Use vty_buf_put.
(vty_insert_word_overwrite) Length check needs to leave room for nul.
(*) Add vty_buf_assert calls.